Electroluminescent host material

ABSTRACT

An OLED device comprises a cathode, an anode, and has therebetween a light-emitting layer containing a phosphorescent emitter and a host comprising a first aluminum or gallium complex containing at least one 2-(2-hydroxyphenyl)pyridine ligand and at least one phenoxy ligand,
         wherein the phenoxy ligand is substituted by an amine or there is further present adjacent to the light-emitting layer on the cathode side a layer containing a second aluminum or gallium complex containing at least one 2-(2-hydroxyphenyl)pyridine ligand and at least one phenoxy ligand.

FIELD OF INVENTION

This invention relates to organic electroluminescent (EL) devicescontaining a light emitting layer including a phosphorescent emitter anda particular aluminum or gallium complex host. More specifically, thisinvention relates to efficient and low voltage phosphorescent ELdevices.

BACKGROUND OF THE INVENTION

While organic electroluminescent (EL) devices have been known for overtwo decades, their performance limitations have represented a barrier tomany desirable applications. In simplest form, an organic EL device iscomprised of an anode for hole injection, a cathode for electroninjection, and an organic medium sandwiched between these electrodes tosupport charge recombination that yields emission of light. Thesedevices are also commonly referred to as organic light-emitting diodes,or OLEDs. Representative of earlier organic EL devices are Gurnee et al.U.S. Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No.3,173,050, issued Mar. 9, 1965; Dresner, “Double InjectionElectroluminescence in Anthracene”, RCA Review, Vol. 30, pp. 322-334,1969; and Dresner U.S. Pat. No. 3,710,167, issued Jan. 9, 1973. Theorganic layers in these devices, usually composed of a polycyclicaromatic hydrocarbon, were very thick (much greater than 1 μm).Consequently, operating voltages were very high, often >100V.

More recent organic EL devices include an organic EL element consistingof extremely thin layers (e.g. <1.0 μm) between the anode and thecathode. Herein, the term “organic EL element” encompasses the layersbetween the anode and cathode electrodes. Reducing the thickness loweredthe resistance of the organic layer and has enabled devices that operateat a much lower voltage. In a basic two-layer EL device structure,described first in U.S. Pat. No. 4,356,429, one organic layer of the ELelement adjacent to the anode is specifically chosen to transport holes,therefore, it is referred to as the hole-transporting layer, and theother organic layer is specifically chosen to transport electrons,referred to as the electron-transporting layer. Recombination of theinjected holes and electrons within the organic EL element results inefficient electroluminescence.

There have also been proposed three-layer organic EL devices thatcontain an organic light-emitting layer (LEL) between thehole-transporting layer and electron-transporting layer, such as thatdisclosed by Tang et al [J. Applied Physics, Vol. 65, Pages 3610-3616,1989]. The light-emitting layer commonly consists of a host materialdoped with a guest material. Still further, there has been proposed inU.S. Pat. No. 4,769,292 a four-layer EL element comprising ahole-injecting layer (HIL), a hole-transporting layer (HTL), alight-emitting layer (LEL) and an electron transport/injection layer(ETL). These structures have resulted in improved device efficiency.

Many emitting materials that have been described as useful in an OLEDdevice emit light from their excited singlet state by fluorescence. Theexcited singlet state is created when excitons formed in an OLED devicetransfer their energy to the excited state of the dopant. However, it isgenerally believed that only 25% of the excitons created in an EL deviceare singlet excitons. The remaining excitons are triplet, which cannotreadily transfer their energy to the singlet excited state of a dopant.This results in a large loss in efficiency since 75% of the excitons arenot used in the light emission process.

Triplet excitons can transfer their energy to a dopant if it has atriplet excited state that is low enough in energy. If the triplet stateof the dopant is emissive it can produce light by phosphorescence. Inmany cases singlet excitons can also transfer their energy to lowestsinglet excited state of the same dopant. The singlet excited state canoften relax, by an intersystem crossing process, to the emissive tripletexcited state. Thus, it is possible, by the proper choice of host anddopant, to collect energy from both the singlet and triplet excitonscreated in an OLED device and to produce a very efficient phosphorescentemission.

The light-emitting layer is typically composed of a host material and adopant. Aluminum complexes are not common materials for use as a hostmaterial in phosphorescent devices. However their use in combinationwith a particular electron transporting material has been described inUS2004/0124769. An example of an aluminum complex as the entirelight-emitting layer has also been disclosed in JP200357588.

A hole-blocking layer (HBL) located between the LEL and the ETL is oftenuseful to confine holes to the LEL, to help confine the excitons orelectron-hole recombination centers to the light emitting layer. Oneexample of a hole-blocking material isbis(2-methyl-8-quinolinolato)(4-phenylphenolato)Aluminum(III) (BalQ);other aluminum compounds are disclosed in US2005/0019605.

Notwithstanding these developments, there remains a need for newcomplexes that will function as triplet host and hole-blocking materialsin electroluminescent devices having improved efficient and low drivevoltage.

SUMMARY OF THE INVENTION

The invention provides an OLED device comprising a cathode, an anode,and having therebetween a light-emitting layer containing aphosphorescent emitter and a host comprising a first aluminum or galliumcomplex containing at least one 2-(2-hydroxyphenyl)pyridine ligand andat least one phenoxy ligand, wherein the phenoxy ligand is substitutedby an amine or there is further present adjacent to the light-emittinglayer on the cathode side a layer containing a second aluminum orgallium complex containing at least one 2-(2-hydroxyphenyl)pyridineligand and at least one phenoxy ligand.

The devices of the invention exhibit improved luminance efficiencyand/or low drive voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a schematic of a typical OLED device ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment A

The invention provides an OLED device comprising a cathode, an anode,and having therebetween a light-emitting layer containing aphosphorescent emitter and a host comprising a first aluminum or galliumcomplex containing at least one 2-(2-hydroxyphenyl)pyridine ligand andat least one phenoxy ligand, wherein there is further present adjacentto the light-emitting layer on the cathode side a layer containing asecond aluminum or gallium complex containing at least one2-(2-hydroxyphenyl)pyridine ligand and at least one phenoxy ligand.

In one embodiment the first complex is an aluminum complex. In additionit is possible for the first and second complexes to be the samecompound. The emitter in the light-emitting layer may be an iridiumphosphorescent emitter.

Suitably, the first complex is represented by Formula I:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to 5. In a preferred embodiment, R² is a phenyl or arylamine group.

Phenoxypyridine ligands have higher triplet energy than variousquinolates such as those in Alq and BAlq. Even higher triplet energiescan be achieved by placing substituents, particularly ortho substituentswhich will induce twisting of the bond between the phenol and pyridinerings of the ligand.

In another embodiment, the first complex is represented by Formula II:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is independently 0 to 5.

In another embodiment, the first complex is represented by Formula III:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to 5.

In a preferred embodiment, the second complex is represented by FormulaI:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to 5.

In another preferred embodiment, the second complex is represented byFormula III:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to 5.

Embodiment B

In another embodiment, the OLED devices comprises a cathode, an anode,and having therebetween a light-emitting layer containing aphosphorescent emitter and a host comprising a first aluminum or galliumcomplex containing at least one 2-(2-hydroxyphenyl)pyridine ligand andat least one phenoxy ligand substituted with an amine. The emitter inthe light-emitting layer may be an iridium phosphorescent emitter.Suitably, the amine is selected from pyridine, pyrrole, and indole.

In one embodiment, the first complex is represented by Formula IV:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is independently 0 to 5.

In a preferred embodiment the first complex is represented by FormulaII:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is independently 0 to 5.

In a more preferred embodiment, there is further present adjacent to thelight-emitting layer on the cathode side a layer containing a secondaluminum or gallium complex containing at least one2-(2-hydroxyphenyl)pyridine ligand and at least one phenoxy ligand.

The second complex may be represented by Formula III:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to 5.

Embodiments of the invention may provide advantageous features such asoperating efficiency, higher luminance, color hue, low drive voltage,and improved operating stability. Embodiments of the organometalliccompounds useful in the invention may provide a wide range of huesincluding those useful in the emission of white light (directly orthrough filters to provide multicolor displays).

Unless otherwise specifically stated, use of the term “substituted” or“substituent” means any group or atom other than hydrogen. Additionally,when the term “group” is used, it means that when a substituent groupcontains a substitutable hydrogen, it is also intended to encompass notonly the substituent's unsubstituted form, but also its form furthersubstituted with any substituent group or groups as herein mentioned, solong as the substituent does not destroy properties necessary for deviceutility. Suitably, a substituent group may be halogen or may be bondedto the remainder of the molecule by an atom of carbon, silicon, oxygen,nitrogen, phosphorous, sulfur, selenium, or boron. The substituent maybe, for example, halogen, such as chloro, bromo or fluoro; nitro;hydroxyl; cyano; carboxyl; or groups which may be further substituted,such as alkyl, including straight or branched chain or cyclic alkyl,such as methyl, trifluoromethyl, ethyl, t-butyl,3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such asethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy,2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy,2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such asphenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, suchas phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy;carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido,alpha-(2,4-di-t-pentyl-phenoxy)acetamido,alpha-(2,4-di-t-pentylphenoxy)butyramido,alpha-(3-pentadecylphenoxy)-hexanamido,alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl,N-methyltetradecanamido, N-succinimido, N-phthalimido,2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, andN-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,benzyloxycarbonylamino, hexadecyloxycarbonylamino,2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino,2,5-(di-t-pentylphenyl)carbonylamino,p-dodecyl-phenylcarbonylamino,p-tolylcarbonyl amino, N-methylureido, N,N-dimethylureido,N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido,N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido,N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido;sulfonamido, such as methylsulfonamido, benzenesulfonamido,p-tolylsulfonamido, p-dodecylbenzenesulfonamido,N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, andhexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl,N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, suchas N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such asacetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such asmethoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,2-ethylhexyloxysulfonyl, phenoxysulfonyl,2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl; sulfonyloxy,such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such asmethylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl,hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, andp-tolylsulfinyl; thio, such as ethylthio, octylthio, benzylthio,tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such asacetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy;amine, such as phenylanilino, 2-chloroanilino, diethylamine,dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or3-benzylhydantoinyl; phosphate, such as dimethylphosphate andethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; aheterocyclic group, a heterocyclic oxy group or a heterocyclic thiogroup, each of which may be substituted and which contain a 3 to 7membered heterocyclic ring composed of carbon atoms and at least onehetero atom selected from the group consisting of oxygen, nitrogen,sulfur or phosphorous, such as pyridyl, thienyl, furyl, azolyl,thiazolyl, oxazolyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl,pyrolidinonyl, quinolinyl, isoquinolinyl, 2-furyl, 2-thienyl,2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such astriethylammonium; quaternary phosphonium, such as triphenylphosphonium;and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted oneor more times with the described substituent groups. The particularsubstituents used may be selected by those skilled in the art to attaindesirable properties for a specific application and can include, forexample, electron-withdrawing groups, electron-donating groups, andsteric groups. When a molecule may have two or more substituents, thesubstituents may be joined together to form a ring such as a fused ringunless otherwise provided. Generally, the above groups and substituentsthereof may include those having up to 48 carbon atoms, typically 1 to36 carbon atoms and usually less than 24 carbon atoms, but greaternumbers are possible depending on the particular substituents selected.

For the purpose of this invention, also included in the definition of aheterocyclic ring are those rings that include coordinate or dativebonds. The definition of a coordinate bond can be found in Grant &Hackh's Chemical Dictionary, page 91. In essence, a coordinate bond isformed when electron rich atoms such as O or N, donate a pair ofelectrons to electron deficient atoms such as Al or B.

It is well within the skill of the art to determine whether a particulargroup is electron donating or electron accepting. The most commonmeasure of electron donating and accepting properties is in terms ofHammett σ values. Hydrogen has a Hammett σ value of zero, while electrondonating groups have negative Hammett σ values and electron acceptinggroups have positive Hammett σ values. Lange's handbook of Chemistry,12^(th) Ed., McGraw Hill, 1979, Table 3-12, pp. 3-134 to 3-138, hereincorporated by reference, lists Hammett σ values for a large number ofcommonly encountered groups. Hammett σ values are assigned based onphenyl ring substitution, but they provide a practical guide forqualitatively selecting electron donating and accepting groups.

Suitable electron donating groups may be selected from —R′, —OR′, and—NR′(R″) where R′ is a hydrocarbon containing up to 6 carbon atoms andR″ is hydrogen or R′. Specific examples of electron donating groupsinclude methyl, ethyl, phenyl, methoxy, ethoxy, phenoxy, —N(CH₃)₂,—N(CH₂CH₃)₂, —NHCH₃, —N(C₆H₅)₂, —N(CH₃)(C₆H₅), and —NHC₆H₅.

Suitable electron accepting groups may be selected from the groupconsisting of cyano, α-haloalkyl, α-haloalkoxy, amido, sulfonyl,carbonyl, carbonyloxy and oxycarbonyl substituents containing up to 10carbon atoms. Specific examples include —CN, —F, —CF₃, —OCF₃, —CONHC₆H₅,—SO₂C₆H₅, —COC₆H₅, —CO₂C₆H₅, and —OCOC₆H₅.

Unless otherwise specified, the term “percentage” or “percent” and thesymbol “%” of a material indicates the volume percent of the material inthe layer in which it is present.

Compounds useful in this invention include:

General Device Architecture

The present invention can be employed in many OLED device configurationsusing small molecule materials, oligomeric materials, polymericmaterials, or combinations thereof. These include very simple structurescomprising a single anode and cathode to more complex devices, such aspassive matrix displays comprised of orthogonal arrays of anodes andcathodes to form pixels, and active-matrix displays where each pixel iscontrolled independently, for example, with thin film transistors(TFTs).

There are numerous configurations of the organic layers wherein thepresent invention can be successfully practiced. The essentialrequirements of an OLED are an anode, a cathode, and an organiclight-emitting layer located between the anode and cathode. Additionallayers may be employed as more fully described hereafter.

A typical structure, especially useful for of a small molecule device,is shown in FIG. 1 and is comprised of a substrate 101, an anode 103, ahole-injecting layer 105, a hole-transporting layer 107, excitonblocking layer, 108, a light-emitting layer 109, a hole- orexciton-blocking layer 110, an electron-transporting layer 111, and acathode 113. These layers are described in detail below. Note that thesubstrate may alternatively be located adjacent to the cathode, or thesubstrate may actually constitute the anode or cathode. The organiclayers between the anode and cathode are conveniently referred to as theorganic EL element. Also, the total combined thickness of the organiclayers is desirably less than 500 nm.

The anode and cathode of the OLED are connected to a voltage/currentsource 150 through electrical conductors 160. The OLED is operated byapplying a potential between the anode and cathode such that the anodeis at a more positive potential than the cathode. Holes are injectedinto the organic EL element from the anode and electrons are injectedinto the organic EL element at the cathode. Enhanced device stabilitycan sometimes be achieved when the OLED is operated in an AC mode where,for some time period in the cycle, the potential bias is reversed and nocurrent flows. An example of an AC driven OLED is described in U.S. Pat.No. 5,552,678.

Substrate

The OLED device of this invention is typically provided over asupporting substrate 101 where either the cathode or anode can be incontact with the substrate. The substrate can be a complex structurecomprising multiple layers of materials. This is typically the case foractive matrix substrates wherein TFTs are provided below the OLEDlayers. It is still necessary that the substrate, at least in theemissive pixilated areas, be comprised of largely transparent materials.The electrode in contact with the substrate is conveniently referred toas the bottom electrode. Conventionally, the bottom electrode is theanode, but this invention is not limited to that configuration. Thesubstrate can either be light transmissive or opaque, depending on theintended direction of light emission. The light transmissive property isdesirable for viewing the EL emission through the substrate. Transparentglass or plastic is commonly employed in such cases. For applicationswhere the EL emission is viewed through the top electrode, thetransmissive characteristic of the bottom support can be lighttransmissive, light absorbing or light reflective. Substrates for use inthis case include, but are not limited to, glass, plastic, semiconductormaterials, silicon, ceramics, and circuit board materials. It isnecessary to provide in these device configurations a light-transparenttop electrode.

Anode

When the desired electroluminescent light emission (EL) is viewedthrough the anode, the anode 103 should be transparent or substantiallytransparent to the emission of interest. Common transparent anodematerials used in this invention are indium-tin oxide (ITO), indium-zincoxide (IZO) and tin oxide, but other metal oxides can work including,but not limited to, aluminum- or indium-doped zinc oxide,magnesium-indium oxide, and nickel-tungsten oxide. In addition to theseoxides, metal nitrides, such as gallium nitride, and metal selenides,such as zinc selenide, and metal sulfides, such as zinc sulfide, can beused as the anode. For applications where EL emission is viewed onlythrough the cathode, any conductive material can be used, transparent,opaque or reflective. Example conductors for this application include,but are not limited to, gold, iridium, molybdenum, palladium, andplatinum. Typical anode materials, transmissive or otherwise, have awork function of 4.1 eV or greater. Desired anode materials are commonlydeposited by any suitable means such as evaporation, sputtering,chemical vapor deposition, or electrochemical means. Anodes can bepatterned using well-known photolithographic processes. Optionally,anodes may be polished prior to application of other layers to reducesurface roughness so as to minimize shorts or enhance reflectivity.

Hole-Injecting Layer (HIL)

A hole-injecting layer 105 may be provided between the anode and thehole-transporting layer. The hole-injecting material can serve toimprove the film formation property of subsequent organic layers and tofacilitate injection of holes into the hole-transporting layer. Suitablematerials for use in the hole-injecting layer include, but are notlimited to, porphyrinic compounds as described in U.S. Pat. No.4,720,432, plasma-deposited fluorocarbon polymers as described in U.S.Pat. No. 6,127,004, U.S. Pat. No. 6,208,075 and U.S. Pat. No. 6,208,077,some aromatic amines, for example, MTDATA(4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine), and inorganicoxides including vanadium oxide (VOx), molybdenum oxide (MoOx), andnickel oxide (NiOx). Alternative hole-injecting materials reportedlyuseful in organic EL devices are described in EP 0 891 121 A1 and EP 1029 909 A1.

The thickness of a hole injection layer containing a plasma-depositedfluorocarbon polymer can be in the range of 0.2 nm to 15 nm and suitablyin the range of 0.3 to 1.5 nm.

Hole-Transporting Layer (HTL)

It is usually advantageous to have a hole transporting layer 107deposited between the anode and the emissive layer. A hole transportingmaterial deposited in said hole transporting layer between the anode andthe light emitting layer may be the same or different from a holetransporting compound used as a co-host or in exciton blocking layeraccording to the invention. The hole transporting layer may optionallyinclude a hole injection layer. The hole transporting layer may includemore than one hole transporting compound, deposited as a blend ordivided into separate layers.

The hole-transporting layer contains at least one hole-transportingcompound such as an aromatic tertiary amine, where the latter isunderstood to be a compound containing at least one trivalent nitrogenatom that is bonded only to carbon atoms, at least one of which is amember of an aromatic ring. In one form the aromatic tertiary amine canbe an arylamine, such as a monoarylamine, diarylamine, triarylamine, ora polymeric arylamine. Exemplary monomeric triarylamines are illustratedby Klupfel et al. U.S. Pat. No. 3,180,730. Other suitable triarylaminessubstituted with one or more vinyl radicals and/or comprising at leastone active hydrogen containing group are disclosed by Brantley et alU.S. Pat. Nos. 3,567,450 and 3,658,520.

A more preferred class of aromatic tertiary amines is those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. No. 4,720,432 and U.S. Pat. No. 5,061,569. Such compoundsinclude those represented by structural formula (HT1):

wherein

Q₁ and Q₂ are independently selected aromatic tertiary amine moieties,and G is a linking group such as an arylene, cycloalkylene, or alkylenegroup of a carbon to carbon bond. In one embodiment, at least one of Q₁or Q₂ contains a polycyclic fused ring structure, e.g., a naphthalene.When G is an aryl group, it is conveniently a phenylene, biphenylene, ornaphthalene moiety. A useful class of triarylamines satisfyingstructural formula (HT1) and containing two triarylamine moieties isrepresented by structural formula (HT2):

wherein

R₁ and R₂ each independently represents a hydrogen atom, an aryl group,or an alkyl group or R₁ and R₂ together represent the atoms completing acycloalkyl group; and

R₃ and R₄ each independently represents an aryl group, which is in turnsubstituted with a diaryl substituted amino group, as indicated bystructural formula (HT3):

wherein

R₅ and R₆ are independently selected aryl groups. In one embodiment, atleast one of R₅ or R₆ contains a polycyclic fused ring structure, e.g.,a naphthalene.

Another class of aromatic tertiary amines is the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by formula (HT3), linked through an arylene group. Usefultetraaryldiamines include those represented by formula (HT4):

wherein

each Are is an independently selected arylene group, such as a phenyleneor anthracene moiety,

n is an integer of from 1 to 4, and

R₁, R₂, R₃, and R₄ are independently selected aryl groups. In a typicalembodiment, at least one of R₁, R₂, R₃, and R₄ is a polycyclic fusedring structure, e.g., a naphthalene.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural formulae (HT1), (HT2), (HT3), (HT4) can each in turn besubstituted. Typical substituents include alkyl groups, alkoxy groups,aryl groups, aryloxy groups, and halide such as fluoride, chloride, andbromide. The various alkyl and alkylene moieties typically contain fromabout 1 to 6 carbon atoms. The cycloalkyl moieties can contain from 3 toabout 10 carbon atoms, but typically contain five, six, or seven ringcarbon atoms, such as cyclopentyl, cyclohexyl, and cycloheptyl ringstructures. The aryl and arylene moieties are usually phenyl andphenylene moieties.

The hole transporting layer can be formed of a single tertiary aminecompound or a mixture of such compounds. Specifically, one may employ atriarylamine, such as a triarylamine satisfying the formula (HT2), incombination with a tetraaryldiamine, such as indicated by formula (HT4).Illustrative of useful aromatic tertiary amines are the following:

-   1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC);-   1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;-   N,N,N′,N′-tetraphenyl-4,4′″-diamino-1,1′:4′,1″:4″,1′″-quaterphenyl;-   Bis(4-dimethylamino-2-methylphenyl)phenylmethane;-   1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (BDTAPVB);-   N,N,N′,N′-Tetra-p-tolyl-4,4′-diaminobiphenyl;-   N,N,N′,N′-Tetraphenyl-4,4′-diaminobiphenyl;-   N,N,N′,N′-tetra-1-naphthyl-4,4′-diaminobiphenyl;-   N,N,N′,N′-tetra-2-naphthyl-4,4′-diaminobiphenyl;-   N-Phenylcarbazole;-   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB);-   4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD);-   4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB);-   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl;-   4,4′-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl;-   1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene;-   4,4′-Bis[N-(9-anthryl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl;-   4,4′-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl;-   2,6-Bis(di-p-tolylamino)naphthalene;-   2,6-Bis[di-(1-naphthyl)amino]naphthalene;-   2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene;-   N,N,N′,N′-Tetra(2-naphthyl)-4,4″-diamino-p-terphenyl;-   4,4′-Bis {N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl;-   2,6-Bis[N,N-di(2-naphthyl)amino]fluorine;-   4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine(MTDATA);-   N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl-N′-(3-methylphenyl)-N′-phenyl-1,4-benzenediamine;-   4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine    (TCTA);-   4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-benzenamine;-   9,9′-(2,2′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis-9H-carbazole    (CDBP);-   9,9′-[1,1′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP);-   9,9′-(1,3-phenylene)bis-9H-carbazole (mCP);-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;-   9,9′-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine.    Another class of useful hole-transporting materials includes    polycyclic aromatic compounds as described in EP 1 009 041. Some    hole-injecting materials described in EP 0 891 121 A1 and EP 1 029    909 A1, can also make useful hole-transporting materials. In    addition, polymeric hole-transporting materials can be used    including poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole,    polyaniline, and copolymers including    poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also    called PEDOT/PSS.    Exciton Blocking Layer

An OLED device according to the invention may include one or moreexciton blocking layers, 108 (FIG. 1), placed adjacent the lightemitting layer 109 on the anode side, to help confine triplet excitonsto the light emitting layer. For the exciton blocking layer to becapable of confining triplet excitons, the material or materials of thislayer should have triplet energies that exceed that of thephosphorescent emitter. If the triplet energy level of any material inthe layer adjacent the light emitting layer is lower than that of thephosphorescent emitter, often that material will quench excited statesin the light emitting layer, decreasing device luminous efficiency. In apreferred embodiment, the exciton blocking layer also helps to confineelectron-hole recombination events to the light emitting layer byblocking the escape of electrons from the light emitting layer into theexciton blocking layer. In order for the exciton blocking layer to havethis electron blocking property, the material of this layer should havea lowest unoccupied molecular orbital (LUMO) energy level that isgreater than that of the host material in the light emitting layer by atleast 0.2 eV. In an embodiment wherein the host comprises a mixture ofhost materials, the LUMO energy level of the exciton block should begreater by at least 0.2 eV than that of the host material having thelowest LUMO energy level in order to have the preferred electronblocking property.

The relative energy levels of the highest occupied molecular orbital(HOMO) and the LUMO of materials may be estimated by several methodsknown in the art. When comparing energy levels of two materials, it isimportant to use estimated energy levels obtained by the same method foreach. Two methods for estimating the HOMO energy level include measuringthe ionization potential of the material by ultraviolet photoelectronspectroscopy and measuring the oxidation potential by an electrochemicaltechnique such as cyclic voltammetry. The LUMO energy level may then beestimated by adding the optical band gap energy to the previouslydetermined HOMO energy level. The optical band gap is estimated to bethe energy difference between the LUMO and the HOMO. The relative LUMOenergy levels of materials may also be estimated from reductionpotentials of the materials measured in solution by an electrochemicaltechnique such as cyclic voltammetry.

We have found that luminous yield and power efficiency in the OLEDdevice employing a phosphorescent emitter in the light emitting layercan be improved significantly if the selected exciton blocking materialor materials have a triplet energy greater or equal to 2.5 eV,especially for the case of green or blue-emitting phosphorescentemitters.

The exciton blocking layer is often between 1 and 500 nm thick andsuitably between 10 and 300 nm thick. Thicknesses in this range arerelatively easy to control in manufacturing. In addition to having hightriplet energy, the exciton blocking layer 108 must be capable oftransporting holes to the light emitting layer 109. Exciton blockinglayer 108 can be used alone or with a hole-transporting layer 107. Theexciton blocking layer may include more than one compound, deposited asa blend or divided into separate layers. In an embodiment wherein a holetransporting compound is used as a host or co-host, a hole transportingmaterial deposited in the exciton blocking layer between the anode andthe light emitting layer may be the same or different from the holetransporting compound used as a host or co-host. The exciton blockingmaterial can comprise compounds containing one or more triarylaminegroups, provided that their triplet energy exceeds that of thephosphorescent material. In a preferred embodiment the triplet energy isgreater or equal to 2.5 eV. To meet the triplet energy requirement forthe preferred embodiment of 2.5 eV or greater, said compounds should notcontain aromatic hydrocarbon fused rings (e.g., a naphthalene group).

The substituted triarylamines that function as the exciton blockingmaterial in the present invention may be selected from compounds havingthe chemical formula (EBF-1):

In formula (EBF-1), Are is independently selected from alkyl,substituted alkyl, aryl, or substituted aryl group;

R₁-R₄ are independently selected aryl groups;

n is an integer of from 1 to 4.

In a preferred embodiment, Are and R₁-R₄ do not include aromatichydrocarbon fused rings.

Example materials useful in the exciton blocking layer 108 include, butare not limited to:

-   2,2′-dimethyl-N,N,N′,N′-tetrakis(4-methylphenyl)-1,1′-biphenyl-4,4′-diamine.-   4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (MTDATA);-   4,4′,4″-tris(N,N-diphenyl-amino)triphenylamine (TDATA);-   N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl-N′-(3-methylphenyl)-N′-phenyl-1,4-benzenediamine.

In one desirable embodiment the material in the exciton blocking layeris selected from formula (EBF-2):

In formula (EBF-2), R₁ and R₂ represent substituents, provided that R₁and R₂ can join to form a ring. For example, R₁ and R₂ can be methylgroups or join to form a cyclohexyl ring. Ar₁-Ar₄ representindependently selected aromatic groups, for example phenyl groups ortolyl groups. R₃-R₁₀ independently represent hydrogen, alkyl,substituted alkyl, aryl, substituted aryl group. In one desirableembodiment, R₁-R₂, Ar₁-Ar₄ and R₃-R₁₀ do not contain fused aromaticrings.

Some non-limiting examples of such materials are:

-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)cyclohexane (TAPC);-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)cyclopentane;-   4,4′-(9H-fluoren-9-ylidene)bis[N,N-bis(4-methylphenyl)-benzenamine;-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-4-phenylcyclohexane;-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-4-methylcyclohexane;-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-3-phenylpropane;-   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylpenyl)methane;-   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)ethane;-   4-(4-Diethylaminophenyl)triphenylmethane;-   4,4′-Bis(4-diethylaminophenyl)diphenylmethane.

In one suitable embodiment the exciton blocking material comprises amaterial of formula (EBF-3):

wherein n is an integer from 1 to 4;Q is N, C, aryl, or substituted aryl group;R₁ is phenyl, substituted phenyl, biphenyl, substituted biphenyl, arylor substituted aryl;R₂ through R₇ are independently hydrogen, alkyl, phenyl or substitutedphenyl, aryl amine, carbazole, or substituted carbazole; provided thatR₂-R₇ do not contain aromatic hydrocarbon fused rings.

Some non-limiting examples of such materials are:

-   4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine    (TCTA);-   4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-benzenamine;-   9,9′-[5′-[4-(9H-carbazol-9-yl)phenyl][1,1′:3′,1″-terphenyl]-4,4″-diyl]bis-9H-carbazole.

In one suitable embodiment the exciton blocking material comprises amaterial of formula (EBF-4):

wherein n is an integer from 1 to 4;

Q is phenyl, substituted phenyl, biphenyl, substituted biphenyl, aryl,or substituted aryl group;

R₁ through R₆ are independently hydrogen, alkyl, phenyl or substitutedphenyl, aryl amine, carbazole, or substituted carbazole;

provided that R₁-R₆ do not contain aromatic hydrocarbon fused rings.

Non-limiting examples of suitable materials are:

-   9,9′-(2,2′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis-9H-carbazole    (CDBP);-   9,9′-[1,1′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP);-   9,9′-(1,3-phenylene)bis-9H-carbazole (mCP);-   9,9′-(1,4-phenylene)bis-9H-carbazole;-   9,9′,9″-(1,3,5-benzenetriyl)tris-9H-carbazole;-   9,9′-(1,4-phenylene)bis[N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;-   9,9′-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine;-   9-phenyl-9H-carbazol.

Metal complexes may also serve as exciton blocking layers as long asthey have the desired triplet energies and hole transport and electronblocking properties. An example of this is,fac-tris(1-phenylpyrazolato-N,C2)iridium(III) (Ir(ppz)₃), as describedin US 20030175553.

Light-Emitting Layer (LEL)

Suitably, the light-emitting layer of the OLED device comprises one ormore host materials and one or more guest materials for emitting light.At least one of the guest materials is suitably a fluorescent orphosphorescent material. The light-emitting guest material(s) is usuallypresent in an amount less than the amount of host materials and istypically present in an amount of up to 20 wt % of the host, moretypically from 0.1-10 wt % of the host. For convenience, thelight-emitting guest material may be referred to as a light emittingdopant. A phosphorescent guest material may be referred to herein as aphosphorescent material, or phosphorescent dopant. The phosphorescentmaterial is preferably a low molecular weight compound, but it may alsobe an oligomer or a polymer. It may be provided as a discrete materialdispersed in the host material, or it may be bonded in some way to thehost material, for example, covalently bonded into a polymeric host.

Fluorescent materials may be used in the same layer as thephosphorescent material, in adjacent layers, in adjacent pixels, or anycombination. Care must be taken to select materials that will notadversely affect the performance of the phosphorescent materials of thisinvention. One skilled in the art will understand that concentrationsand triplet energies of materials in the same layer as thephosphorescent material or in an adjacent layer must be appropriatelyset so as to prevent unwanted quenching of the phosphorescence.

Host Materials for Phosphorescent Materials

Suitable host materials have a triplet energy (the difference in energybetween the lowest triplet excited state and the singlet ground state ofthe host) that is greater than or equal to the triplet energy of thephosphorescent emitter. This energy level state is necessary so thattriplet excitons are transferred to the phosphorescent emitter moleculesand any triplet excitons formed directly on the phosphorescent emittermolecules remain until emission occurs. However, efficient emission fromdevices in which the host material has a lower triplet energy than thephosphorescent emitter is still possible in some cases as reported by C.Adachi, et al Appl. Phys. Lett., 79 2082-2084 (2001). Triplet energy isconveniently measured by any of several means, as discussed for instancein S. L. Murov, I. Carmichael, and G. L. Hug, Handbook ofPhotochemistry, 2nd ed. (Marcel Dekker, New York, 1993).

In the absence of experimental data the triplet energies may beestimated in the following manner. The triplet state energy for amolecule is defined as the difference between the ground state energy(E(gs)) of the molecule and the energy of the lowest triplet state(E(ts)) of the molecule, both given in eV. These energies can becalculated using the B3LYP method as implemented in the Gaussian98(Gaussian, Inc., Pittsburgh, Pa.) computer program. The basis set foruse with the B3LYP method is defined as follows: MIDI! for all atoms forwhich MIDI! is defined, 6-31G* for all atoms defined in 6-31G* but notin MIDI!, and either the LACV3P or the LANL2DZ basis set andpseudopotential for atoms not defined in MIDI! or 6-31G*, with LACV3Pbeing the preferred method. For any remaining atoms, any published basisset and pseudopotential may be used. MIDI!, 6-31G* and LANL2DZ are usedas implemented in the Gaussian98 computer code and LACV3P is used asimplemented in the Jaguar 4.1 (Schrodinger, Inc., Portland Oreg.)computer code. The energy of each state is computed at theminimum-energy geometry for that state. The difference in energy betweenthe two states is further modified by Equation 1 to give the tripletstate energy (E(t)):E(t)=0.84*(E(ts)−E(gs))+0.35  (1)

For polymeric or oligomeric materials, it is sufficient to compute thetriplet energy over a monomer or oligomer of sufficient size so thatadditional units do not substantially change the computed triplet energyof the material.

Desirable host materials are capable of forming a continuous film. Thelight-emitting layer may contain more than one host material in order toimprove the device's film morphology, electrical properties, lightemission efficiency, and lifetime. Suitable host materials are describedin WO00/70655; WO01/39234; WO01/93642; WO02/074015; WO02/15645, andUS20020117662.

Types of triplet host materials may be categorized according to theircharge transport properties. The two major types are those that arepredominantly electron-transporting and those that are predominantlyhole-transporting. It should be noted that some host materials which maybe categorized as transporting dominantly one type of charge, maytransport both types of charges, especially in certain devicestructures, for example CBP which is described in C. Adachi, R. Kwong,and S. R. Forrest, Organic Electronics, 2, 37-43 (2001). Another type ofhost are those having a wide energy gap between the HOMO and LUMO suchthat they do not readily transport charges of either type and insteadrely on charge injection directly into the phosphorescent dopantmolecules.

A desirable electron transporting host may be any suitable electrontransporting compound, such as benzazole, phenanthroline,1,3,4-oxadiazole, triazole, triazine, or triarylborane, as long as ithas a triplet energy that is higher than that of the phosphorescentemitter to be employed.

A preferred class of benzazoles is described by Jianmin Shi et al. inU.S. Pat. No. 5,645,948 and U.S. Pat. No. 5,766,779. Such compounds arerepresented by structural formula (PHF-1):

In formula (PHF-1), n is selected from 2 to 8;

Z is independently O, NR or S;

R and R′ are individually hydrogen; alkyl of from 1 to 24 carbon atoms,for example, propyl, t-butyl, heptyl, and the like; aryl or hetero-atomsubstituted aryl of from 5 to 20 carbon atoms, for example, phenyl andnaphthyl, furyl, thienyl, pyridyl, quinolinyl and other heterocyclicsystems; or halo such as chloro, fluoro; or atoms necessary to completea fused aromatic ring; and

X is a linkage unit consisting of carbon, alkyl, aryl, substitutedalkyl, or substituted aryl, which conjugately or unconjugately connectsthe multiple benzazoles together.

An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)represented by a formula (PHF-2) shown below:

Another class of the electron transporting materials suitable for use asa host includes various substituted phenanthrolines as represented byformula (PHF-3):

In formula (PHF-3), R₁-R₈ are independently hydrogen, alkyl group, arylor substituted aryl group, and at least one of R₁-R₈ is aryl group orsubstituted aryl group.

Examples of suitable materials are2,9-dimethyl-4,7-diphenyl-phenanthroline (BCP) (see formula (PH-1)) and4,7-diphenyl-1,10-phenanthroline (Bphen) (see formula (PH-2)).

A triarylboranes that functions as an electron transporting host may beselected from compounds having the chemical formula (PHF-4):

wherein

Ar₁ to Ar₃ are independently an aromatic hydrocarbocyclic group or anaromatic heterocyclic group which may have one or more substituent. Itis preferable that compounds having the above structure are selectedfrom formula (PHF-5):

wherein R₁-R₁₅ are independently hydrogen, fluoro, cyano,trifluoromethyl, sulfonyl, alkyl, aryl or substituted aryl group.

Specific representative embodiments of the triarylboranes include:

An electron transporting host may be selected from substituted1,3,4-oxadiazoles. Illustrative of the useful substituted oxadiazolesare the following:

An electron transporting host may be selected from substituted1,2,4-triazoles. An example of a useful triazole is3-phenyl-4-(1-naphtyl)-5-phenyl-1,2,4-triazole represented by formula(PHF-6):

The electron transporting host may be selected from substituted1,3,5-triazines. Examples of suitable materials are:

-   2,4,6-tris(diphenylamino)-1,3,5-triazine;-   2,4,6-tricarbazolo-1,3,5-triazine;-   2,4,6-tris(N-phenyl-2-naphthylamino)-1,3,5-triazine;-   2,4,6-tris(N-phenyl-1-naphthylamino)-1,3,5-triazine;-   4,4′,6,6′-tetraphenyl-2,2′-bi-1,3,5-triazine;-   2,4,6-tris([1,1′:3′,1″-terphenyl]-5′-yl)-1,3,5-triazine.

In one embodiment, a suitable host material is an aluminum or galliumcomplex. Particularly useful hosts materials are represented by Formula(PHF-7).

In Formula (PHF-7), M₁ represents Al or Ga. R₂-R₇ represent hydrogen oran independently selected substituent. Desirably, R₂ represents anelectron-donating group, such as a methyl group. Suitably, R₃ and R₄each independently represent hydrogen or an electron donatingsubstituent. Preferably, R₅, R₆, and R₇ each independently representhydrogen or an electron-accepting group. Adjacent substituents, R₂-R₇,may combine to form a ring group. L is an aromatic moiety linked to thealuminum by oxygen, which may be substituted with substituent groupssuch that L has from 6 to 30 carbon atoms. Illustrative examples ofFormula (PHF-7) materials are listed below.

A desirable hole transporting host may be any suitable hole transportingcompound, such as a triarylamine or a carbazole, as long it has atriplet energy higher than that of the phosphorescent emitter to beemployed. A suitable class of hole transporting compounds for use as ahost are aromatic tertiary amines, by which it is understood to becompounds containing at least one trivalent nitrogen atom that is bondedonly to carbon atoms, at least one of which is a member of an aromaticring. In one form the aromatic tertiary amine can be an arylamine, suchas a monoarylamine, diarylamine, triarylamine, or a polymeric arylamine.Exemplary monomeric triarylamines are illustrated by Klupfel et al. inU.S. Pat. No. 3,180,730. Other suitable triarylamines substituted withone or more vinyl radicals and/or comprising at least one activehydrogen containing group are disclosed by Brantley et al. in U.S. Pat.No. 3,567,450 and U.S. Pat. No. 3,658,520.

A more preferred class of aromatic tertiary amines are those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. No. 4,720,432 and U.S. Pat. No. 5,061,569. Such as thetetraaryldiamines. Desirable tetraaryldiamines include two diarylaminogroups, such as indicated by formula (PHF-8):

wherein each Are is an independently selected arylene group, such as aphenylene or anthracene moiety,

n is selected from 1 to 4, and

R₁-R₄ are independently selected aryl groups.

In a typical embodiment, at least one of R₁-R₄ is a polycyclic fusedring structure, e.g., a naphthalene. However, when the emission of thedopant is blue or green in color it is less preferred to have an arylamine host material to have a polycyclic fused ring substituent.

Representative examples of the useful compounds include the following:

-   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB);-   4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB);-   4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD);-   4,4′-Bis-diphenylamino-terphenyl;-   2,6,2′,6′-tetramethyl-N,N,N′,N′-tetraphenyl-benzidine.4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine    (MTDATA);-   4,4′,4″-tris(N,N-diphenyl-amino) triphenylamine (TDATA);-   N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl-N′-(3-methylphenyl)-N′-phenyl-1,4-benzenediamine.

In one desirable embodiment the hole transporting host comprises amaterial of formula (PHF-9):

In formula (PHF-9), R₁ and R₂ represent substituents, provided that R₁and R₂ can join to form a ring. For example, R₁ and R₂ can be methylgroups or join to form a cyclohexyl ring;

Ar₁-Ar₄ represent independently selected aromatic groups, for examplephenyl groups or tolyl groups;

R₃-R₁₀ independently represent hydrogen, alkyl, substituted alkyl, aryl,substituted aryl group.

Examples of suitable materials include, but are not limited to:

-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)cyclohexane (TAPC);-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)cyclopentane;-   4,4′-(9H-fluoren-9-ylidene)bis[N,N-bis(4-methylphenyl)-benzenamine;-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-4-phenylcyclohexane;-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-4-methylcyclohexane;-   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-3-phenylpropane;-   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylpenyl)methane;-   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)ethane;-   4-(4-Diethylaminophenyl)triphenylmethane;-   4,4′-Bis(4-diethylaminophenyl)diphenylmethane.

A useful class of compounds for use as the hole transporting hostincludes carbazole derivatives such as those represented by formula(PHF-10):

In formula (PHF-10), Q independently represents nitrogen, carbon,silicon, a substituted silicon group, an aryl group, or substituted arylgroup, preferably a phenyl group;

R₁ is preferably an aryl or substituted aryl group, and more preferablya phenyl group, substituted phenyl, biphenyl, substituted biphenylgroup;

R₂ through R₇ are independently hydrogen, alkyl, phenyl or substitutedphenyl group, aryl amine, carbazole, or substituted carbazole;

and n is selected from 1 to 4.

Illustrative useful substituted carbazoles are the following:

-   4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine    (TCTA);-   4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-benzenamine;-   9,9′-[5′-[4-(9H-carbazol-9-yl)phenyl][1,1′:3′,1″-terphenyl]-4,4″-diyl]bis-9H-carbazole.-   3,5-bis(9-carbazolyl)tetraphenylsilane (SimCP).

In one suitable embodiment the hole transporting host comprises amaterial of formula (PHF-11):

In formula (PHF-11), n is selected from 1 to 4;

Q independently represents phenyl group, substituted phenyl group,biphenyl, substituted biphenyl group, aryl, or substituted aryl group;

R₁ through R₆ are independently hydrogen, alkyl, phenyl or substitutedphenyl, aryl amine, carbazole, or substituted carbazole.

Examples of suitable materials are the following:

-   9,9′-(2,2′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis-9H-carbazole    (CDBP);-   9,9′-[1,1′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP);-   9,9′-(1,3-phenylene)bis-9H-carbazole (mCP);-   9,9′-(1,4-phenylene)bis-9H-carbazole;-   9,9′,9″-(1,3,5-benzenetriyl)tris-9H-carbazole;-   9,9′-(1,4-phenylene)bis[N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;-   9,9′-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine.

Host materials which are electron transporting or hole transporting withsome electron transporting properties, such as carbazoles, are generallymore desirable when used as a single host material. This is especiallytrue for typical phosphorescent dopants that are hole-trapping orcapable of accepting injected holes. Less preferable are host materialswhich are primarily hole transporting and have little electrontransporting properties, such as triarlyamines. Iinjecting electronsinto these latter hole transporting hosts may be difficult because oftheir relatively high LUMO energies.

Host materials may comprise a mixture of two or more host materials.Particularly useful is a mixture comprising at least one each of anelectron-transporting and a hole-transporting co-host. The optimumconcentration of the hole transporting co-host(s) may be determined byexperimentation and may be within the range 10 to 60 weight % of thetotal of the hole- and electron transporting co-host materials in thelight emitting layer, and is often found to be in the range 15 to 30 wt.%. It is further noted that electron-transporting molecules andhole-transporting molecules may be covalently joined together to formsingle host molecules having both electron-transporting andhole-transporting properties.

A wide energy gap host material may be any suitable compound having alarge HOMO-LUMO gap such that the HOMO and LUMO of the phosphorescentemissive material are within the HOMO and LUMO for the host. In thiscase, the phosphorescent emissive material acts as the primary chargecarrier for both electrons and holes, as well as the site for thetrapping of excitons. Often the phosphorescent dopants for use with thewide energy gap hosts are selected to have electron-withdrawingsubstituents to facilitate electron injection. The “wide energy gap”host material functions as a non-charge carrying material in the system.Such a combination may lead to high operation voltage of the device, asthe concentration of the charge-carrying dopant is typically below 10%in the emissive layer.

Thompson et al. disclosed in US 2004/0209115 and US 2004/0209116 a groupof wide energy gap hosts having triplet energies suitable for bluephosphorescent OLEDs. Such compounds include those represented bystructural formula (PHF-12):

wherein:

X is Si or Pb; Ar₁, Ar₂, Ar₃ and Ar₄ are each an aromatic groupindependently selected from phenyl and high triplet energy heterocyclicgroups such as pyridine, pyrazole, thiophene, etc. It is believed thatthe HOMO-LUMO gaps in these materials is large due to the electronicallyisolated aromatic units, and the lack of any conjugating substituents.

Illustrative examples of this type of hosts include:

Phosphorescent Materials

Phosphorescent materials may be used singly or in combination with otherphosphorescent materials, either in the same or different layers. Someother phosphorescent materials are described in WO 00/57676, WO00/70655, WO 01/41512, WO 02/15645, US 2003/0017361, WO 01/93642, WO01/39234, U.S. Pat. No. 6,458,475, WO 02/071813, U.S. Pat. No.6,573,651, US 2002/0197511, WO 02/074015, U.S. Pat. No. 6,451,455, US2003/0072964, US 2003/0068528, U.S. Pat. No. 6,413,656, U.S. Pat. No.6,515,298, U.S. Pat. No. 6,451,415, U.S. Pat. No. 6,097,147, US2003/0124381, US 2003/0059646, US 2003/0054198, EP 1 239 526, EP 1 238981, EP 1 244 155, US 2002/0100906, US 2003/0068526, US 2003/0068535, JP2003073387, JP 2003073388, US 2003/0141809, US 2003/0040627, JP2003059667, JP 2003073665, and US 2002/0121638.

In many known hosts and device architectures for phosphorescent OLEDs,the optimum concentration of the phosphorescent dopant for luminousefficiency is found to be about 1 to 20 vol % and often 6 to 8 vol %relative to the host material. However, in a preferred embodiment,wherein the host comprises at least one electron-transporting co-hostand at least one hole-transporting co-host in the light-emitting layer,a phosphorescent material concentration from about 0.5% to about 6%often provides high luminous efficiencies.

The emission wavelengths of cyclometallated Ir(III) complexes of thetype IrL₃ and IrL₂L′, such as the green-emittingfac-tris(2-phenylpyridinato-N,C^(2′))Iridium(III) (Ir(ppy)₃) andbis(2-phenylpyridinato-N,C^(2′))Iridium(III)(acetylacetonate) may beshifted by substitution of electron donating or withdrawing groups atappropriate positions on the cyclometallating ligand L, or by choice ofdifferent heterocycles for the cyclometallating ligand L. The emissionwavelengths may also be shifted by choice of the ancillary ligand L′.Examples of red emitters are thebis(2-(2′-benzothienyl)pyridinato-N,C^(3′))Iridium(III)(acetylacetonate)and tris(2-phenylisoquinolinato-N,C)Iridium(III). A blue-emittingexample isbis(2-(4,6-diflourophenyl)-pyridinato-N,C^(2′))Iridium(III)(picolinate).

Red electrophosphorescence has been reported, usingbis(2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C³) iridium (acetylacetonate)[Btp₂Ir(acac)] as the phosphorescent material (Adachi, C., Lamansky, S.,Baldo, M. A., Kwong, R. C., Thompson, M. E., and Forrest, S. R., App.Phys. Lett., 78, 1622-1624 (2001).

Other important phosphorescent materials include cyclometallated Pt(II)complexes such as cis-bis(2-phenylpyridinato-N,C^(2′))platinum(II),cis-bis(2-(2′-thienyl)pyridinato-N,C^(3′)) platinum(II),cis-bis(2-(2′-thienyl)quinolinato-N,C^(5′)) platinum(II), or(2-(4,6-diflourophenyl)pyridinato-NC2′) platinum (II) acetylacetonate.Pt(II) porphyrin complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) are also useful phosphorescent materials.

Still other examples of useful phosphorescent materials includecoordination complexes of the trivalent lanthanides such as Tb³⁺ andEu³⁺ (J. Kido et al, Appl. Phys. Lett., 65, 2124 (1994))

Blocking Layers

In addition to suitable hosts and transporting materials, an OLED deviceemploying a phosphorescent material often requires at least one excitonor hole blocking layer to help confine the excitons or electron-holerecombination centers to the light emitting layer comprising the hostand phosphorescent material. In one embodiment, such a blocking layer110 would be placed between the electron transporting layer and thelight emitting layer—see FIG. 1. In this case, the ionization potentialof the blocking layer should be such that there is an energy barrier forhole migration from the light emitting layer into theelectron-transporting layer, while the electron affinity should be suchthat electrons pass readily from the electron transporting layer intothe light emitting layer. It is further desired, but not absolutelyrequired, that the triplet energy of the blocking material be greaterthan that of the phosphorescent material. Suitable hole blockingmaterials are described in WO 00/70655 and WO 01/93642. Two examples ofuseful materials are bathocuproine (BCP) andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)Aluminum(III) (BAlQ).Metal complexes other than BAlQ are also known to block holes andexcitons as described in US 20030068528. US 20030175553 describes theuse of fac-tris(1-phenylpyrazolato-N,C2)iridium(III) (Irppz) in anelectron/exciton blocking layer.

Electron-Transporting Layer (ETL)

The electron transporting material deposited in said electrontransporting layer between the cathode and the light emitting layer maybe the same or different from an electron transporting co-host material.The electron transporting layer may include more than one electrontransporting compound, deposited as a blend or divided into separatelayers.

Preferred thin film-forming materials for use in constructing theelectron transporting layer of the organic EL devices of this inventionare metal-chelated oxinoid compounds, including chelates of oxine itself(also commonly referred to as 8-quinolinol or 8-hydroxyquinoline). Suchcompounds help to inject and transport electrons, exhibiting high levelsof performance, and are readily fabricated in the form of thin films.Exemplary of contemplated oxinoid compounds are those satisfyingstructural formula (ET1) below:

wherein

M represents a metal;

n is an integer of from 1 to 4; and

Z independently in each occurrence represents the atoms completing anucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be monovalent,divalent, trivalent, or tetravalent metal. The metal can, for example,be an alkali metal, such as lithium, sodium, or potassium; an alkalineearth metal, such as magnesium or calcium; an earth metal, such aluminumor gallium, or a transition metal such as zinc or zirconium. Generallyany monovalent, divalent, trivalent, or tetravalent metal known to be auseful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

Illustrative of useful chelated oxinoid compounds are the following:

CO-1: Aluminum trisoxine [alias, tris(8-quinolinolato)aluminum(III);Alq];

CO-2: Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)];

CO-3: Bis[benzo {f}-8-quinolinolato]zinc (II);

CO-4:Bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)aluminum(III);

CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium];

CO-6: Aluminum tris(5-methyloxine) [alias,tris(5-methyl-8-quinolinolato) aluminum(III)];

CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)];

CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)];

CO-9: Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)].

Other electron transporting materials suitable for use in the electrontransporting layer include various butadiene derivatives as disclosed inU.S. Pat. No. 4,356,429 and various heterocyclic optical brighteners asdescribed in U.S. Pat. No. 4,539,507. Benzazoles satisfying structuralformula (ET2) are also useful electron transporting materials:

wherein

n is an integer of 3 to 8;

Z is O, NR or S; and

R and R′ are individually hydrogen; alkyl of from 1 to 24 carbon atoms,for example, propyl, t-butyl, heptyl, and the like; aryl or hetero-atomsubstituted aryl of from 5 to 20 carbon atoms for example phenyl andnaphthyl, furyl, thienyl, pyridyl, quinolinyl and other heterocyclicsystems; or halo such as chloro, fluoro; or atoms necessary to completea fused aromatic ring; and

X is a linkage unit consisting of carbon, alkyl, aryl, substitutedalkyl, or substituted aryl, which conjugately or unconjugately connectsthe multiple benzazoles together. An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)disclosed in Shi et al. in U.S. Pat. No. 5,766,779.

Other electron transporting materials suitable for use in the electrontransporting layer may be selected from triazines, triazoles,imidazoles, oxazoles, thiazoles and their derivatives,polybenzobisazoles, pyridine- and quinoline-based materials,cyano-containing polymers and perfluorinated materials.

The electron transporting layer or a portion of the electrontransporting layer adjacent the cathode may further be doped with analkali metal to reduce electron injection barriers and hence lower thedrive voltage of the device. Suitable alkali metals for this purposeinclude lithium and cesium.

Cathode

When light emission is viewed solely through the anode 103, the cathodeused in this invention can be comprised of nearly any conductivematerial. Desirable materials have good film-forming properties toensure good contact with the underlying organic layer, promote electroninjection at low voltage, and have good stability. Useful cathodematerials often contain a low work function metal (<4.0 eV) or metalalloy. One useful cathode material is comprised of a Mg:Ag alloy whereinthe percentage of silver is in the range of 1 to 20%, as described inU.S. Pat. No. 4,885,221. Another suitable class of cathode materialsincludes bilayers comprising a thin electron-injection layer (EIL) incontact with an organic layer (e.g., an electron transporting layer(ETL)) which is capped with a thicker layer of a conductive metal. Here,the EIL preferably includes a low work function metal or metal salt, andif so, the thicker capping layer does not need to have a low workfunction. One such cathode is comprised of a thin layer of LiF followedby a thicker layer of Al as described in U.S. Pat. No. 5,677,572. An ETLmaterial doped with an alkali metal, for example, Li-doped Alq, asdisclosed in U.S. Pat. No. 6,013,384, is another example of a usefulEIL. Other useful cathode material sets include, but are not limited to,those disclosed in U.S. Pat. Nos. 5,059,861, 5,059,862, and 6,140,763.

When light emission is viewed through the cathode, the cathode must betransparent or nearly transparent. For such applications, metals must bethin or one must use transparent conductive oxides, or a combination ofthese materials. Optically transparent cathodes have been described inmore detail in U.S. Pat. No. 4,885,211, U.S. Pat. No. 5,247,190, JP3,234,963, U.S. Pat. No. 5,703,436, U.S. Pat. No. 5,608,287, U.S. Pat.No. 5,837,391, U.S. Pat. No. 5,677,572, U.S. Pat. No. 5,776,622, U.S.Pat. No. 5,776,623, U.S. Pat. No. 5,714,838, U.S. Pat. No. 5,969,474,U.S. Pat. No. 5,739,545, U.S. Pat. No. 5,981,306, U.S. Pat. No.6,137,223, U.S. Pat. No. 6,140,763, U.S. Pat. No. 6,172,459, EP 1 076368, U.S. Pat. No. 6,278,236, and U.S. Pat. No. 6,284,393. Cathodematerials are typically deposited by any suitable methods such asevaporation, sputtering, or chemical vapor deposition. When needed,patterning can be achieved through many well known methods including,but not limited to, through-mask deposition, integral shadow masking asdescribed in U.S. Pat. No. 5,276,380 and EP 0 732 868, laser ablation,and selective chemical vapor deposition.

Other Common Organic Layers and Device Architecture

In some instances, layers 109 and 111 can optionally be collapsed into asingle layer that serves the function of supporting both light emissionand electron transportation. It also known in the art that emittingdopants may be added to the hole-transporting layer, which may serve asa host. Multiple dopants may be added to one or more layers in order tocreate a white-emitting OLED, for example, by combining blue- andyellow-emitting materials, cyan- and red-emitting materials, or red-,green-, and blue-emitting materials. White-emitting devices aredescribed, for example, in EP 1 187 235, EP 1 182 244, U.S. Pat. No.5,683,823, U.S. Pat. No. 5,503,910, U.S. Pat. No. 5,405,709, and U.S.Pat. No. 5,283,182, US 20020186214, US 20020025419, US 20040009367, andU.S. Pat. No. 6,627,333.

Additional layers such as exciton, electron and hole-blocking layers astaught in the art may be employed in devices of this invention.Hole-blocking layers are commonly used to improve efficiency ofphosphorescent emitter devices, for example, as in US 20020015859, WO00/70655A2, WO 01/93642A1, US 20030068528 and US 20030175553 A1

This invention may be used in so-called stacked device architecture, forexample, as taught in U.S. Pat. No. 5,703,436 and U.S. Pat. No.6,337,492.

Deposition of Organic Layers

The organic materials mentioned above are suitably deposited through avapor-phase method such as sublimation, but can be deposited from afluid, for example, from a solvent with an optional binder to improvefilm formation. If the material is a polymer, solvent deposition isuseful but other methods can be used, such as sputtering or thermaltransfer from a donor sheet. The material to be deposited by sublimationcan be vaporized from a sublimation “boat” often comprised of a tantalummaterial, e.g., as described in U.S. Pat. No. 6,237,529, or can be firstcoated onto a donor sheet and then sublimed in closer proximity to thesubstrate. Layers with a mixture of materials can utilize separatesublimation boats or the materials can be pre-mixed and coated from asingle boat or donor sheet. Patterned deposition can be achieved usingshadow masks, integral shadow masks (U.S. Pat. No. 5,294,870),spatially-defined thermal dye transfer from a donor sheet (U.S. Pat.Nos. 5,688,551, 5,851,709 and 6,066,357) and inkjet method (U.S. Pat.No. 6,066,357).

One preferred method for depositing the materials of the presentinvention is described in US 2004/0255857 and U.S. Ser. No. 10/945,941where different source evaporators are used to evaporate each of thematerials of the present invention. A second preferred method involvesthe use of flash evaporation where materials are metered along amaterial feed path in which the material feed path is temperaturecontrolled. Such a preferred method is described in the followingco-assigned patent applications: U.S. Ser. No. 10/784,585; U.S. Ser. No.10/805,980; U.S. Ser. No. 10/945,940; U.S. Ser. No. 10/945,941; U.S.Ser. No. 11/050,924; and U.S. Ser. No. 11/050,934. Using this secondmethod, each material may be evaporated using different sourceevaporators or the solid materials may be mixed prior to evaporationusing the same source evaporator.

Encapsulation

Most OLED devices are sensitive to moisture or oxygen, or both, so theyare commonly sealed in an inert atmosphere such as nitrogen or argon. Insealing an OLED device in an inert environment, a protective cover canbe attached using an organic adhesive, a metal solder, or a low meltingtemperature glass. Commonly, a getter or desiccant is also providedwithin the sealed space. Useful getters and desiccants include, alkaliand alkaline metals, alumina, bauxite, calcium sulfate, clays, silicagel, zeolites, alkaline metal oxides, alkaline earth metal oxides,sulfates, or metal halides and perchlorates. Methods for encapsulationand desiccation include, but are not limited to, those described in U.S.Pat. No. 6,226,890. In addition, barrier layers such as SiOx, Teflon,and alternating inorganic/polymeric layers are known in the art forencapsulation.

Optical Optimization

OLED devices of this invention can employ various well-known opticaleffects in order to enhance its properties if desired. This includesoptimizing layer thicknesses to yield maximum light transmission,providing dielectric mirror structures, replacing reflective electrodeswith light-absorbing electrodes, providing anti glare or anti-reflectioncoatings over the display, providing a polarizing medium over thedisplay, or providing colored, neutral density, or color conversionfilters in functional relationship with the light emitting areas of thedisplay. Filters, polarizers, and anti-glare or anti-reflection coatingscan also be provided over a cover or as part of a cover.

The OLED device may have a microcavity structure. In one useful example,one of the metallic electrodes is essentially opaque and reflective; theother one is reflective and semitransparent. The reflective electrode ispreferably selected from Au, Ag, Mg, Ca, or alloys thereof. Because ofthe presence of the two reflecting metal electrodes, the device has amicrocavity structure. The strong optical interference in this structureresults in a resonance condition. Emission near the resonance wavelengthis enhanced and emission away from the resonance wavelength isdepressed. The optical path length can be tuned by selecting thethickness of the organic layers or by placing a transparent opticalspacer between the electrodes. For example, an OLED device of thisinvention can have ITO spacer layer placed between a reflective anodeand the organic EL media, with a semitransparent cathode over theorganic EL media.

EXAMPLES Example 1

An EL device satisfying the requirements of the invention wasconstructed in the following manner:

-   -   1. A glass substrate coated with an 85 nm layer of indium-tin        oxide (ITO) as the anode was sequentially ultrasonicated in a        commercial detergent, rinsed in deionized water, degreased in        toluene vapor and exposed to oxygen plasma for about 1 min.    -   2. Over the ITO was deposited a 1 nm fluorocarbon (CFx)        hole-injecting layer (HIL) by plasma-assisted deposition of        CHF₃.    -   3. A hole-transporting layer (HTL) of        N,N′-di-1-naphthyl-N,N′-diphenyl-4,4′-diaminobiphenyl (NPB)        having a thickness of 75 nm was then evaporated from a tantalum        boat.    -   4. A 35 nm light-emitting layer (LEL) of Inv-2 and        fac-tris(2-phenyl-pyridinato-N^C-)Iridium(III) (Ir(ppy)₃) (6 wt        %) were then deposited onto the hole-transporting layer. These        materials were also evaporated from tantalum boats.    -   5. A hole-blocking layer of Inv-2 having a thickness of 10 nm        was then evaporated from a tantalum boat.    -   6. A 40 nm electron-transporting layer (ETL) of        tris(8-quinolinolato)aluminum (III) (AlQ₃) was then deposited        onto the hole-blocking layer. This material was also evaporated        from a tantalum boat.    -   7. On top of the AIQ₃ layer was deposited a 220 nm cathode        formed of a 10:1 volume ratio of Mg and Ag.

The above sequence completed the deposition of the EL device. The devicewas then hermetically packaged in a dry glove box for protection againstambient environment.

Example 2 was fabricated in an identical manner to Example 1 exceptbis(2-methyl-quinolinolato)(2,4,6-triphenylphenolato)aluminum(III)(BAlq) was used in the hole blocking layer in place of Inv-2.

Example 3 was fabricated in an identical manner to Example 1 except CBPwas used in emissive layer in place of Inv-2, and BCP was used in thehole blocking layer in place of Inv-2.

Example 4 was fabricated in an identical manner to Example 1 exceptmixture of 70% CBP and 30% Alq was used in emissive layer in place ofInv-2 and BCP was used in the hole blocking layer in place of Inv-2.

The sample cells thus formed were measured for efficiency and voltage at20 mA/cm², and the results are shown in Table I.

TABLE I Example Voltage (V) cd/m² 1 13 4298 2 13.4 4170 3 12.8 3390 412.8 74

Comparing example 1 and 2 illustrates the lower voltage and higherluminance efficiency benefit of using Inv-2 as the hole blocking layerinstead of BAlq. Comparing examples 3 and 4 shows that the use of Alq inan emissive layer greatly reduces the device efficiency. This problem isnot present in Examples 1 and 2, and highlights the benefits of usingInv-2 in the emissive layer and Inv-2 in the hole blocking layer insteadof using Alq in the emissive layer and BCP in the hole blocking layer.

Example 5

An EL device satisfying the requirements of the invention wasconstructed in the following manner:

-   -   1. A glass substrate coated with an 85 nm layer of indium-tin        oxide (ITO) as the anode was sequentially ultrasonicated in a        commercial detergent, rinsed in deionized water, degreased in        toluene vapor and exposed to oxygen plasma for about 1 min.    -   2. Over the ITO was deposited a 1 nm fluorocarbon (CFx)        hole-injecting layer (HIL) by plasma-assisted deposition of        CHF₃.    -   3. A hole-transporting layer (HTL) of        N,N′-di-1-naphthyl-N,N′-diphenyl-4,4′-diaminobiphenyl (NPB)        having a thickness of 75 nm was then evaporated from a tantalum        boat.    -   4. A 35 nm light-emitting layer (LEL) of Inv-13 and Ir(ppy)₃ (6        wt %) were then deposited onto the hole-transporting layer.        These materials were also evaporated from tantalum boats.    -   5. A hole-blocking layer of Inv-2 having a thickness of 10 nm        was then evaporated from a tantalum boat.    -   6. A 40 nm electron-transporting layer (ETL) of        tris(8-quinolinolato)aluminum (III) (AlQ₃) was then deposited        onto the hole-blocking layer. This material was also evaporated        from a tantalum boat.    -   7. On top of the AlQ₃ layer was deposited a 220 nm cathode        formed of a 10:1 volume ratio of Mg and Ag.

The above sequence completed the deposition of the EL device. The devicewas then hermetically packaged in a dry glove box for protection againstambient environment.

Example 6 was fabricated in an identical manner to Example 5 exceptIr(ppy)₃ was used in the LEL at 12 wt % instead of 6 wt %.

Example 7 was fabricated in an identical manner to Example 5 exceptbis(2-methyl-quinolinolato)(2,4,6-triphenylphenolato)aluminum(III)(BAlq) was used in the hole blocking layer in place of Inv-2. The samplecells thus formed were measured for efficiency and voltage at 20 mA/cm²,the results are shown in Table II.

TABLE II Example Voltage (V) cd/m² 5 8.73 4487 6 8.83 4590 7 9.43 1726

Comparing examples 5 and 6 with example 7 illustrates the benefit ofusing Inv-2 as the hole blocking layer instead of BAlq. Theconcentration of the dopant may be varied from 6 to 12 wt % in Example 5vs. 6, and the efficiency and voltage improvement does not changesignificantly.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. The entire contents of the patents and otherpublications referred to in this specification are incorporated hereinby reference.

PARTS LIST

-   101 Substrate-   103 Anode-   105 Hole-Injecting layer (HIL)-   107 Hole-Transporting layer (HTL)-   108 Exciton Blocking Layer (EBL)-   109 Light-Emitting layer (LEL)-   110 Hole Blocking Layer (HBL)-   111 Electron-Transporting layer (ETL)-   113 Cathode-   150 Current/Voltage source-   160 Electrical conductors

1. An OLED device comprising a cathode, an anode, and havingtherebetween a light-emitting layer containing a phosphorescent emitterand a host comprising a first aluminum or gallium complex represented byFormula II:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is independently 0 to 5, wherein there is further presentadjacent to the light-emitting layer on the cathode side a layercontaining a second aluminum or gallium complex containing at least one2-(2-hydroxyphenyl)pyridine ligand and at least one phenoxy ligand. 2.An OLED device of claim 1, wherein the first and second complexes arethe same compound.
 3. An OLED device of claim 1, wherein thelight-emitting layer contains an iridium-containing phosphorescentemitter.
 4. An OLED device of claim 1, wherein the second complex isrepresented by Formula I:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fined rings; n is independently 0to 4; and m is 0 to
 5. 5. An OLED device of claim 1, wherein the secondcomplex is represented by Formula III:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to
 5. 6. An OLED device comprising a cathode, an anode,and having therebetween a light-emitting layer containing aphosphorescent emitter and a host comprising a first aluminum or galliumcomplex containing at least one 2-(2-hydroxyphenyl)pyridine ligand andat least one phenoxy ligand substituted with an amine.
 7. An OLED deviceof claim 6, wherein the light-emitting layer contains aniridium-containing phosphorescent emitter.
 8. An OLED device of claim 6,wherein the amine is selected from one comprising a pyridine, pyrrole,or indole group.
 9. An OLED device of claim 6, wherein the first complexis represented by Formula IV:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is independently 0 to
 5. 10. An OLED device of claim 9,wherein the first complex is represented by Formula II:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is independently 0 to
 5. 11. An OLED device of claim 9,wherein there is further present adjacent to the light-emitting layer onthe cathode side a layer containing a second aluminum or gallium complexcontaining at least one 2-(2-hydroxyphenyl)pyridine ligand and at leastone phenoxy ligand.
 12. An OLED device of claim 11, wherein the secondcomplex is represented by Formula III:

wherein; R¹ and R² are independently selected from alkyl, aryl,heteroaryl, halogen, aryl amine, alkyl amine, and cyano groups, providedthat groups may join together to form fused rings; n is independently 0to 4; and m is 0 to
 5. 13. An OLED device of claim 6 wherein the firstcomplex comprises at least one of the following:


14. An OLED device of claim 1 wherein the first complex comprises atleast one of the following: